The application of a magnetic field and the subsequent measurement of the magnetic resonance properties of a material is well established. When a magnetic field is applied to an atom, either the resonance pattern of the nucleus, more specifically the protons, or of the electrons can be measured. The first application has become known as nuclear resonance (NMR) while the latter is referred to as electron paramagnetic resonance (EPR).
NMR has been widely used in the field of imaging of the human body. In NMR imaging, a relatively high magnetic field, i.e., on the order of 1 T to 4 T, is applied which causes the previously randomly oriented protons to realign and precess at a specific frequency. This frequency is called the Larmor frequency, and it is proportional to the local strength of the magnetic field at the position of the proton. A second magnetic field or burst of energy is applied to increase the energy of the nuclear proton. Typically, the frequency of this second field is in the range of about 1 megahertz (MHz) to 10 gigahertz (GHz). When the second magnetic field or energy source is turned off, the return of the protons to the first alignment state releases energy. Sensors are provided for sensing the rate of relaxation or energy release of the protons and subsequently generating a signal in the time domain that is referred to as the free induction decay (FID) signal. This signal is then analyzed using a Fourier transform to develop a spectrum of signals in the frequency domain. Analytical means may also be provided for receiving and analyzing the signals emitted, discriminating between various peaks, comparing the amplitude or height of various peaks, and/or normalizing the analysis by reference to a standard sample.
The use of NMR has been widely accepted for imaging purposes, because of the non-invasive nature of the technique and because it does not expose the patient to potentially harmful radiation as is used in conventional radiographic imaging. However, NMR imaging apparatuses require large magnetic fields and are usually physically quite large. Additionally, NMR imaging apparatuses have relatively high electrical consumption loads. In general, NMR imaging apparatuses are expensive to both manufacture and operate, and have thus, not been used extensively in areas of diagnosis and treatment.
However, one diagnostic application of NMR has been described in U.S. Pat. No. 5,072,732 issued to Rapoport et al. on Dec. 17, 1991. This patent describes a NMR apparatus which is used for non-invasively testing body fluids for a particular constituent, such as glucose in blood. In this particular NMR apparatus, the device is adapted to receive an extremity of the patient, such as a finger, in order to test the constituents found in the blood. The extremity is exposed to a first magnetic field having a field strength of at least five to six kilogauss. A coil apparatus, comprised of either a single or multiple coil, is used to apply a second field or energy to the test sample. In this particular apparatus, a radio frequency (RF) generator is used to produce this second field or energy. This coil apparatus also functions as the sensor for detecting the energy released (i.e., the FID) until the second field or energy is removed. Analytical means (i.e., electronic circuitry) are connected to the sensor coils for receiving and analyzing the signals emitted, discriminating between various peaks, comparing the amplitude or height of the various peaks that are attributed to the various constituents such as water and glucose, and for normalizing the analysis by reference to a standard sample so as to obtain the concentration of constituents in the tested materials. In using this particular NMR apparatus, a standard sample containing predetermined amounts of the materials to be tested is placed in the device and measured. This field measurement is compared against a previously stored, known spectrum for the particular constituent in order to normalize and quantify the substance being tested in the body fluid.
As noted previously, the second type of magnetic resonance technology involves measuring the resonance properties of electrons. The measurement of electron paramagnetic resonance is usually made at frequencies in the microwave range, i.e., on the order of 1000 MHz and above. One such electron paramagnetic resonance apparatus, is described in U.S. Pat. No. 4,455,527 issued to Singer on Jun. 19, 1984. In this apparatus, a sample to be measured is placed in a waveguide cavity, which also functions to concentrate the microwaves. The sample can be in several different forms including a solid or liquid of a specific column or weight or a continuous flow of liquid through an electrically insulating conduit. Additionally, this patent teaches that the local magnetic field around the sample must be at a level for which the sample exhibits a maximum resonance absorption. For microwave frequencies, all that is stated in this patent is that this magnetic field is much higher than the magnetic field produced by the earth.
As can be observed from the above discussion, all of the known nuclear and electron magnetic resonance devices require the use of relatively strong magnetic fields, i.e., fields exhibiting at least 100 gauss, but more typically in the 2000-4000 gauss range. In contrast, the magnetic resonance device of the present invention uses a significantly smaller magnetic field, i.e., in the range of 0.5 to 7 gauss.
In addition, the magnetic resonance analyzer of the present invention measures the degree and type of response of the matter under test, and by comparison with reference matter, it assists in recognizing deviations from a desired response. This capability is enhanced by testing with resonance test patterns which relate to the significant characteristics for the particular matter under test. The basis for the magnetic resonance effects of the present invention include proton excitation, manipulation of molecular oscillation, cellular membrane oscillation, and/or electron spin alternation.
Thus, in view of the above differences, the inventive magnetic resonance analyzer offers new advantages in the field of material analysis. Because the present invention uses much lower magnetic fields, it is safer and has less side effects than the prior art devices. In addition, the present inventions have a greater range of applications than the prior art devices and can be optimized for a given task by the use of the proper resonance pattern.